32 



the butterflies begin to lay their eggs on the leaves, one in a place. 

 The eggs are rather smaller than the head of a pin, pale yellow at 

 first, but darker after a few days. They hatch in about a week, 



and the little caterpillars which come from them 

 at once begin to feed on the leaves. At first 

 pale yellow, the caterpillar as it grows becomes 

 velvety green, and when full-grown is more 

 than an inch long. It now crawls to some 

 protected place where it changes to the chrys- 

 alis form — the same as that in which the 

 winter is passed — and becomes quiet while 

 the internal organs of the caterpillar are being 

 built over into those of the adult butterfly. 

 When these changes have been completed the 

 cabbage'worm^a.'fuii. chrysalis bursts open and the adult butterfly 

 grown caterpillar; b, appears, and egg-laying for another brood 

 c iysais - of caterpillars now begins. During the year 



there are three broods of these insects in Massachusetts, the 

 winter being passed in the chrysalis stage. 



Treatment. 



Several methods may be used for controlling this insect. Hot 

 water applied at about 130° will kill the caterpillars usually without 

 injuring the plants, but the disadvantage of this treatment upon a 

 large scale is evident. 



Probably the best method to use is that of spraying with Paris 

 green or Arsenate of lead, as these poisons are very destructive 

 to the caterpillars and without danger to the consumer unless the 

 spraying be done with extreme carelessness and shortly before the 

 heads are cut. There are several reasons why this treatment is not 

 dangerous. The head of the cabbage forms from within, only the 

 very outermost leaves being at any time exposed to the poison, 

 and these are removed in trimming the head for market. Then 

 too, the poison is chiefly needed on the outside leaves of the plant 

 where most of the caterpillars occur, and these leaves are never 

 cut with the head. Chemical analysis of heads heavily sprayed one 

 week before cutting showed that not a trace of arsenic remained. 

 Finally, if spraying be carefully done when the caterpillars first 

 appear in spring and followed up until the head appears, the 

 insect will in all probability be so reduced in numbers that spray- 

 ing after the head is a quarter grown will be unnecessary, thus 

 removing the last possibility of danger. 



This treatment for the cabbage worm is the usual one among 



